1. Field of the Invention
The present invention relates to a droplet discharging head, and more particularly, to a droplet discharging head in a recording head such as a full line type inkjet head, formed to have a long dimension by laminating together thin plates, whereby warping in the longitudinal direction due to internal stress caused by bonding, heat, or the like, is suppressed.
2. Description of the Related Art
Image recording is known which uses a so-called inkjet method, wherein an image is recorded by discharging and propelling ink (ink droplets) from the nozzles of a recording head to deposit the ink onto recording paper, or the like. There are various ink discharge methods for recording heads (inkjet heads) based on an inkjet method. For example, known methods include: a piezoelectric method wherein the volume of a pressure chamber is caused to change by means of deformation of piezoelectric ceramics, ink is introduced into the pressure chamber from an ink supply passage when the volume is increased, and the ink inside the pressure chamber is discharged as a droplet from the nozzle when the volume of the pressure chamber is reduced; an electrostatic method for discharging ink by similarly changing the volume of the pressure chamber; or a thermal inkjet method, or the like, for heating ink and generating bubbles in the ink, and discharging ink by means of the expansive energy created when these bubbles grow, or the like.
For example, an inkjet head using a piezoelectric element has a laminated structure wherein piezoelectric elements, a vibrator plate, a flow passage plate formed with an ink supply passage and pressure chambers, a nozzle plate formed with ink discharge ports (orifice plates), and the like, are layered onto a substrate, the head being manufactured by bonding these thin plates together.
In an inkjet head of this kind formed by a laminated structure of thin plates, if the head has a long dimension, then it is liable to warping in the longitudinal direction, due to internal stress produced by the bonding and heating processes during manufacture. If warping occurs in the inkjet head, then problems occur, for example, the accuracy of the landing positions of the ink droplets discharged from the nozzles deteriorates, and image recording of high quality cannot be achieved, and therefore various methods for preventing warping of this kind have been proposed.
For example, a head is known whereby, in order to restrict the main body of the inkjet print cartridge in the critical direction, which is the direction following the surfaces of the laminated thin plates, after heating and cooling, thereby preventing bending of the nozzle members and separation from the barrier layers, the main body of the cartridge is formed in such a manner that the difference between the coefficient of thermal expansion of the main body of the cartridge in the critical direction and the coefficient of thermal expansion of the nozzle members in the critical direction is within approximately 100 ppm/° C. (see, for example, Japanese Patent Application Publication No. 7-164636).
However, in the technology described in Japanese Patent Application Publication No. 7-164636, even if the difference of the coefficient of thermal expansion is less than 100 ppm, some stress will be generated, and if the head has a long dimension, it will have insufficient strength, and a problem arises in that phenomena, such as warping, curling, and the like, will occur due to the stress generated.
Moreover, although not designed with the particular object of preventing warping, technology relating to a method for manufacturing an inkjet head of long dimension by arranging a plurality of short heads is also known, wherein, when manufacturing a full line type inkjet head of long dimension, by arraying a plurality of base bodies, on which energy converting elements and electrodes corresponding to respective nozzles are formed in an integral manner, on a supporting body, and forming a plurality of discharge ports for discharging ink by bonding with one ceiling plate in which a common liquid chamber, and the like, is formed, the divided base bodies are arrayed at uniform intervals on the supporting body, the plurality of base bodies are cut from the base substrate on which they are arranged, via cutting lines, and the plurality of base bodies thus cut are arranged on the supporting body by positioning the respective cutting lines thereof in a continuous fashion, in such a manner that the pitch error between the base bodies is reduced (see, for example, Japanese Patent Application Publication No. 9-277534).
However, in the technology described in Japanese Patent Application Publication No. 9-277534, the strength of the head is dependent on the strength of the supporting body and the ceiling plate, and since the base bodies are divided, there is liable to be insufficient strength at the connections between the respective base bodies, and warping, and the like, will be generated if the head is formed to have a relatively long dimension.
Furthermore, technology is also known, wherein a foundation plate provided with energy generating elements and a ceiling plate forming an ink passage in conjunction with the foundation plate, are sandwiched between two components (a base plate and ink supply member) made from materials having similar coefficient of thermal expansion (for example, from the same material), and are respectively pressed from either side (for example, screw fastenings, or the like), in such a manner that thermal deformation, warping, and the like, is prevented in the ceiling plate and the foundation plate forming the ink passage (see, for example, Japanese Patent Application Publication No. 2002-67330).
However, in the technology described in Japanese Patent Application Publication No. 2002-67330, a device for pressing the foundation plate and the ceiling plate by means of the base plate and the ink supply member is required, and hence the number of components increases. Moreover, in the technology described in Japanese Patent Application Publication No. 2002-67330, pressure is applied by means of screw fastenings, but a problem arises in that the stress is liable to concentrate in the region of the screws, and hence there is a risk of other damage occurring.
Furthermore, technology is also known wherein a resin section formed with an ink passage and ink discharge ports is taken, and a thermal deformation suppressing member extending in the direction in which the ink discharge ports are arranged, and having a smaller coefficient of thermal expansion than the resin section, is formed in an integral fashion with the resin section, whereby warping and deformation in the longitudinal direction (direction of arrangement of the ink discharge ports) is prevented (for example, Japanese Patent Application Publication No. 2002-210976).
However, in the technology disclosed in Japanese Patent Application Publication No. 2002-210976, since a resin section forming an ink passage and ink discharge ports, and a thermal deformation suppressing member, which is a structural element for reinforcing the strength of same, are formed together in an integral manner, the material is limited to being resin, which does not necessarily have sufficient strength.